Fiber-Optic Broadband Seismometer Based on Inverted Pendulum and Hybrid Interferometer

Broadband seismometers are widely used in seismology and geophysics research. Low self-noise and large dynamic range are required in seismic detection but are limited by the optomechanical design for the newly developed fiber-optic seismometers. A fiber-optic broadband interferometric inverted pendulum seismometer (iIPS) is proposed. It is designed with a cross-spring inverted pendulum and a hybrid Michelson interferometer and provides a simple solution for recording seismic waves. By developing the pendulum and interferometer, iIPS achieves a long-period response of 35043 rad/g within dc ~4 Hz, a self-noise better than the Earth’s new low-noise mode within <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.1\sim 10$ </tex-math></inline-formula> Hz, and a dynamic range of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$160\sim 200$ </tex-math></inline-formula> dB. Earthquake recordings at the Baijiatuan (BJT) seismic station show that the data quality of iIPS is comparable to that of Streckeisen STS-2.5, one of the best seismometers in the world.